The present invention relates to devices and methods for controlling helicopter tail rotor authority and more particularly to devices and methods for automatically altering the maximum input of tail rotor pitch on a helicopter based on altitude and temperature so that as ambient air pressure increases or temperature decreases the maximum input to tail rotor blade angle and authority decreases, and as ambient air pressure decreases or temperature increases the maximum input of tail rotor blade angle and authority increases. The system utilizes a set of proximity sensors which sense the position of a target mounted to an end of a sealed bellows assembly which lengthens or shortens based on atmospheric pressure and temperature changes, the sensors send electrical signals to an array of relays which operate a drive motor altering the geometry of a pivoting linkage member positioned between a manual input linkage and an output linkage while concurrently maintaining alignment of the proximity sensors with the target. The bellows is sealed and charged with a known volume of gas and reacts by lengthening or shortening based on either or both pressure and temperature changes.
Helicopters may be generally group by altitude performance operating limits, which is partly a result of design necessitated by ambient atmospheric conditions encountered. The tail rotor, which produces a maximum sideways thrust known as xe2x80x9ctail rotor authorityxe2x80x9d is likewise designed to operate appropriately in expected ambient atmospheric conditions. A tail rotor and helicopter designed for operating at lower altitudes is unable to maneuver in higher altitudes because the tail rotor pitch angle will not adjust to produce a necessary tail rotor authority, while a tail rotor and helicopter designed for higher altitudes is over designed for lower altitudes. Tail rotor authority is affected by and may be altered by changing one of the following; tail rotor blade size, blade profile, tail rotor blade speed, the angle of attack of the tail rotor blade, the pitch of the tail rotor blades, and air density. In order to safely operate a helicopter in both lower and higher altitudes one or more of the these would need to be altered and of these possibilities it is easiest and preferable to vary the tail rotor blade pitch based on the given air density. Other changes, such as blade profile and size would require the helicopter to be requalified which is not economically feasible. Focusing only on air density with all other factors remaining constant, as air density decreases tail rotor authority decreases, and inversely as air density increases tail rotor authority increases. Air density generally increases as atmospheric pressure increases at lower altitude and temperature and air density decreases as atmospheric pressure decreases at higher altitudes and temperatures. The present invention utilizes a sealed and charged bellows which reacts to ambient air pressure and temperature changes by altering in length. Movement of a target attached to a moving end of the bellows is detected by proximity sensors which in turn activate an array of relays sending electrical signals to a drive motor which varies both the position of the proximity sensors in relation to the target and the pivot position of a pivoting linkage member positioned between an input linkage and an output tail rotor pitch control linkage. Accordingly, movement of the pivot point is directly related to linear movement of the target attached to the moving bellows end via the proximity sensors. The present invention does not utilize a microprocessor or other logic circuit and is thus a simplification of the tail rotor control described by the Russian helicopter manufacturer for its tail rotor pitch foot control dated Jun. 1, 1979 xe2x80x9cservice manualxe2x80x9d and later in U.S. Pat. No. 5,607,122 to Hicks et al. Both the Russian service manual and the Hicks patent disclose a tail rotor authority and control for a helicopter which includes a variable geometry linkage member positioned between the manual tail rotor input linkage and tail rotor angle control, an actuator and a control unit. The actuator changes the configuration of the linkage member variable geometry in response to an actuator movement signal. The control unit includes a microprocessor which receives information concerning ambient conditions from various sensors and calculates and determines a desired actuator position corresponding to a desired maximum tail rotor pitch and provides corresponding actuator movement signals. The Hicks disclosure includes an excellent discussion of the advantages and operation of a variable tail rotor authority control. The present invention differs from Hicks and the Russian service manual in simplification of operation while achieving substantially similar tail rotor authority control limits.
It is thus an object of the invention to provide a helicopter tail rotor authority altitude compensator which automatically alters the maximum input of tail rotor pitch and tail rotor authority on a helicopter based on altitude and temperature so that as ambient air pressure increases or temperature decreases the maximum input to tail rotor blade angle and authority decreases, and as ambient air pressure decreases or temperature increases the maximum input of tail rotor blade angle and authority increases.
It is a further object of the invention to provide a helicopter tail rotor authority altitude compensator which utilizes a single ambient condition sensor in the form of a sealed bellows with a linearly moving end with a target attacked thereto and in alignment with a set of proximity sensors which sense the position of the target, the sensors send electrical signals to an array of relays which operate a drive motor altering the geometry of a pivoting linkage member positioned between a manual input linkage and an output linkage while also aligning and maintaining the target between the proximity sensors. The bellows reacts by lengthening or shortening based on either or both pressure and temperature changes.
It is a still further object of the invention to provide a helicopter tail rotor authority altitude compensator which automatically alters the geometry of the tail rotor pitch input linkage so that an appropriate tail rotor authority may be achieved at various altitudes and temperatures, where at a given ambient atmospheric pressure and temperature, maximum input to the tail rotor control linkage results in a sufficient tail rotor authority for proper control of the helicopter, and as ambient atmospheric pressure or temperature increases or decreases the tail rotor authority altitude compensator alters the input linkage geometry so that sufficient tail rotor authority is achieved at the given atmospheric conditions.
It is a still further object of the invention to provide a helicopter tail rotor authority altitude compensator which is greatly simplified from the prior art and which does not require the use of microprocessors or other logic circuits, which utilizes a single sealed bellows which reacts to both temperature and atmospheric pressure, and which compensator alters the geometry of the tail rotor pitch input linkage in relation to the linear movement of a target attached to a moving end of the sealed bellows.
It is a still further object of the invention to provide a helicopter tail rotor authority altitude compensator with a variable geometry input linkage including a walking beam with an adjustable position center pivot point positioned between an input pivot bearing for connecting a manual tail rotor pitch input control linkage and output pivot bearing for connecting an output tail rotor pitch control linkage, wherein the center pivot point is slidable and variable positioned between the input and output pivot bearing by the rotation of a drive motor which is controlled by the tail rotor altitude compensator and which alters the geometry of the walking beam so that a maximum input tail rotor pitch manual control linkage movement provides a tail rotor authority which is suitable for controlling the helicopter at given atmospheric conditions. The drive motor shaft linearly concurrently moves a proximity sensor mount in parallel alignment with a target mounted to a moving end of a sealed bellows while the target is maintained between proximity sensors mounted to the proximity sensor mount while also slidably and variably moving the center pivot point.